1. Field of the Invention
This invention generally relates to an image intensifying X-ray to visible converter and, more particularly, to such a converter utilizing a photo-electron cathode for the direct conversion of an X-ray image to an electron equivalent image which can be intensified to produce an enhanced real time visible image. A panel type direct view real time X-ray image intensifier with high spatial resolution and high gain has been made by using this new type X-ray photo cathode. A portable low intensity real time projection type X-ray imagescope has also been made by using the new type X-ray image intensifier.
2. Description of the Prior Art
Most of the early X-ray intensifiers are indirect conversion type, wherein the X-ray is converted to visible light in a scintillator, a visible light photo-electron cathode then converts the photons to electrons which are accelerated and multiplied by different techniques, as shown in U.S. Pat. No. 4,104,516, U.S. Pat. No. 4,140,900, U.S. Pat. No. 4,255,666 and U.S. Pat. No. 4,300,046. One commercially available X-ray imagescope employs an unstable radio active isotope X-ray source and an indirect conversion X-ray intensifier which consists of an X-ray scintillator, a pair of fiber-optic plates, a visible light photo-electron cathode, a micro channel plate, a phosphor display screen and a magnifier. There are numerous disadvantages in these prior art X-ray image intensification devices. The most obvious disadvantage being the use of a scintillator, wherein the response time is limited and unsuitable for use in ultrafast X-ray imaging. It is difficult to have both high spatial resolution and high sensitivity. In order to increase sensitivity, the thickness of the scintillator must be increased, which degrades the spatial resolution. Another disadvantage in using scintillators is that they usually are based on a fiber-optic plate which is the input window of a visible light intensifier. These fiber-optic plates must be specially manufactured for reducing the size of the image in order to improve the coupling and the viewing of the field. The complicated techniques for making fiber-optic plates and visible light photo-electron cathodes and the complicated structure of the intensifier itself, make these intensifiers very expensive. On the other hand, the use of these expensive fiber-optic plates also introduce further loss of light intensity and spatial resolution. It is further noted that because of the use of a visible light photo-electron cathode, the intensifier must be light shielded. Still another disadvantage is the inconvenience of using a radio active isotope as the X-ray source. The source not only supplies X-rays during the operation of the device, it also radiates constantly, day and night, and since the energy of the X-ray is not adjustable the isotope usually has a rather short life time.